Filter Additive

ABSTRACT

The present invention relates to a method of producing a filter element for inclusion in a smoking article, the method comprising applying an additive to filter material, the additive being solid at room temperature and the method involving heating the additive so that it melts.

The invention relates to methods for making filter elements and filters for smoking articles, the filter elements and filters comprising an additive material. In particular, the invention relates to methods of incorporating an additive which is solid at room temperature into filter material, the method comprising the step of melting the additive material.

A wide variety of materials have been used as filter materials for tobacco smoke. The most commonly used filter material is cellulose acetate tow. However, whilst cellulose acetate has an excellent capacity to filter tobacco smoke, it has the drawback that it is slower to degrade than other materials and can therefore be disadvantageous environmentally.

Filter materials made from non-woven sheet material and paper are known. Suitable sheet materials include polyvinyl alcohol, reconstituted tobacco, starch, and polylactic acid. These materials are much more readily degradable than cellulose acetate tow, however, they have drawbacks. In particular, in order to attain the desired structural rigidity when constructing a filter element from non-woven sheet materials and paper, the filter material is generally densely packed and this means that these filter elements have quite different properties to those made of cellulose acetate. They exhibit a greater resistance to the flow of smoke, resulting in a pressure drop which is higher than that of a conventional cellulose acetate (CA) filter, requiring the user to draw harder on the smoking article. Perhaps more significantly, the smoke drawn through such filter material has been found to have different taste characteristics compared to the smoke drawn through conventional cellulose acetate filter material. What is more, filter elements comprising non-woven sheet materials or paper as the filter material have been shown to exhibit significantly less selective removal of semi-volatile compounds than conventional cellulose acetate tow filter materials.

It is known to use additives such as triacetin (glycerin triacetate), TEC (triethyl citrate) and PEG 400 (low molecular weight polyethylene glycol) in cellulose acetate filters. These additives function as plasticizers and they are generally used in cellulose acetate filters to give the filter rods sufficient hardness for cigarette manufacture and use. Some plasticizers have the additional advantage of providing cellulose acetate tow with an improved capacity to selectively remove semi-volatile compounds such as phenol, o-cresol, p-cresol and m-cresol from tobacco smoke.

These plasticizers are in liquid form at room temperature and they are sprayed on to cellulose acetate tow. The plasticizer coats the individual fibres within the tow and, with time, they bind or fuse adjacent fibres together at their points of contact, thereby increasing the hardness or rigidity of the filter material, to give the core of the filter the desired structural strength. The mode of action of the plasticizers does, however, mean that there is an upper limit to the amount that may be incorporated into cellulose acetate tow filter material. When above about 7% of plasticizer by weight of the filter is included, the plasticizer starts to have a detrimental effect on the cellulose acetate tow, forming holes which compromises its filtration properties.

Whilst inclusion of plasticizers such as triacetin, TEC or PEG 400 in CA filters is relatively common, their inclusion in non-woven sheet and paper filter materials is less attractive. Firstly, the plasticizers are used in CA filters to bind fibres and the plasticizer would clearly not have this advantageous effect when added to non-woven sheet material or paper (in which the fibres are already bound within the sheet structure). Secondly, these commonly used plasticizers are liquids and their application to non-woven sheet and paper filter materials will be limited as they will cause these materials to become soggy and to lose their structural integrity. Paper, the most commonly used sheet filter material, may start to disintegrate when moist, and will therefore have a reduced acceptability to the user. Furthermore, many sheet materials, including polyvinyl alcohol and polylactic acid, are soluble and therefore the addition of aqueous additives may result in the partial dissolution of the material.

It is therefore an object of the invention to provide a method of constructing a filter element which is more readily degradable than filter elements comprising a conventional cellulose acetate tow as the filter material. Preferably, the method will also result in a filter element which exhibits an improved capacity to selectively remove semi-volatile compounds and which provides smoke having similar taste characteristics to that provided by conventional cellulose acetate filters.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, a method for making a smoking article filter element is provided. The method comprises the steps of:

-   -   i) applying an additive which is solid at room temperature to         the filter material;     -   ii) heating the additive so as to melt it; and     -   iii) forming the filter material and additive into a filter         element.

The steps of the method may be carried out in any order, although in some embodiments, step i) is preferably carried out before step iii).

According to a second aspect of the present invention, a filter element for a smoking article is provided. The filter element comprises filter material and an additive which is solid at room temperature, the filter element being obtained or obtainable by the method according to the first aspect of the present invention.

According to a third aspect of the present invention, a filter for a smoking article is provided, comprising a filter element according to the second aspect.

According to a fourth aspect of the present invention, there is provided a smoking article comprising a filter element according to the second aspect and/or a filter according to the third aspect, attached to a rod of smokeable filler material. The smokeable filler material may comprise tobacco and the smoking article may be a cigarette.

As used herein, the term “smoking article” includes smokeable products such as cigarettes, cigars and cigarillos whether based on tobacco, tobacco derivatives, expanded tobacco, reconstituted tobacco or tobacco substitutes and also heat-not-burn products.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method of producing a filter element for inclusion in a smoking article, the method comprising applying an additive to filter material, the additive being solid at room temperature and the method involving heating the additive so that it melts.

In one embodiment of the invention, the additive is applied to the filter material in solid form, for example in the form of a powder, prior to formation of the filter rod. The formed filter rod may then be heated to melt the additive whilst it remains in contact with the filter material. When the additive material subsequently cools and re-solidifies, it provides the filter material and the filter element formed with one or more of: stability and rigidity; improved smoke taste characteristics; and improved selective removal of semi-volatile compounds.

In an alternative embodiment of the invention, the additive is melted and applied to the filter material in molten or liquid form, prior to formation of the filter rod. When the additive material subsequently cools and re-solidifies, it provides the filter material and the filter element formed with one or more of: stability and rigidity; improved smoke taste characteristics; and improved selective removal of semi-volatile compounds.

The methods according to the present invention may be used to add an additive to any type of filter material, including fibrous filter material or tows, such as conventional cellulose acetate tow which is currently widely used in smoking article filters. However, the method is considered to be particularly effective when it is used to add an additive to alternative filter materials, such as those constructed from a sheet material, for example non-woven sheet materials or paper.

Paper filter material usually comprises gathered, pleated, crimped, crepe or even shredded paper. Paper filter materials tend to have a low air permeability, exhibit a basic pH, and can be gathered or formed easily to form the filter element. A preferred filter material for filter elements of the present invention is a gathered or pleated paper. Examples of suitable papers are Puracel™ and Myria™ papers (Filtrona plc, United Kingdom).

Other, non-woven sheet materials may be used as filter materials. Non-woven materials are broadly defined as sheet or web structures bonded together by entangling fibres or filaments mechanically, thermally or chemically, or by a combination of two or more of these. They tend to be flat, porous sheets that are made directly from separate fibers. They are not made by weaving or knitting and do not require converting the fibers to yarn. The non-woven sheet materials used in the present invention are preferably ones which are readily biodegradable. Examples of materials include polyvinyl alcohol (PVOH), polylactic acid or polylactide (PLA), poly(ε-caprolactone) (PCL), poly(1-4 butanediol succunate) (PBS) and poly(butylene adipate-co-terephthalate) (PBAT). Other suitable filter materials include starch fibres and calcium alginate.

Non-woven sheet materials and paper are more readily biodegradable than cellulose acetate tow. However, they currently have drawbacks when used as filter materials. In order to attain the desired structural rigidity when constructing a filter element from non-woven sheet materials and paper, the filter material must be very densely packed and this means that these filter elements have quite different properties to those made of cellulose acetate. They exhibit a greater resistance to the flow of smoke, resulting in a pressure drop which is higher than that of a conventional cellulose acetate filter, requiring the user to draw harder on the smoking article.

The sheet material used in the method of the invention may comprise paper, polyvinyl alcohol, reconstituted tobacco, starch, or polylactic acid. Preferably the sheet filter material is paper.

Preferred non-woven sheet materials have a thickness greater than about 0.05 mm, preferably from about 0.06 mm to about 0.08 mm. The paper filter materials may comprise paper having a basis weight of about 15 g/m² to about 40 g/m², preferably about 20 g/m² to about 35 g/m².

The sheet material used in the method of the invention may additionally or alternatively comprise polyvinyl alcohol (PVOH). PVOH is unique in being the only biodegradable, carbon-carbon backbone polymer that can completely biodegrade to small molecules, e.g., carbon dioxide and water.

The method may comprise the use of the sheet material polylactic acid. The lactate from which PLA is produced can be derived from the fermentation of agricultural by-products.

However, because of the hygroscopicity of PVOH and PLA, prior art attempts to process such materials have resulted in filter rods which are too soft to be efficiently handled in high speed cigarette manufacturing machines. Furthermore, cigarette filter elements formed from PVOH and PLA have failed to provide a sufficiently stable porous matrix to permit proper draw characteristics and avoid collapse in use. Using the method of the present invention to apply additive, the qualities of these sheet materials may be modified to make them suitable for use in filter elements.

In contrast to the use of additives which are liquid at room temperature (such as the plasticisers frequently used in conventional cellulose acetate filters, including low molecular weight PEG, triacetin and TEC), an additive which is solid at room temperature may provide firmness and rigidity to the filter without damaging the filter material by making it soggy.

Indeed, rather than weakening a non-woven sheet or paper filter material, the method of the present invention uses a solid additive which has been melted, but which re-solidifies at room temperature and bonds parts of the filter material together. Therefore, the additive has the benefit that it can actually increase the structural integrity and rigidity of the filter material. In the case of sheet filter materials, addition of a solid additive by a method according to the present invention may make it possible to use less of the filter material in the filter element. This provides further flexibility when forming the filter element with regard to the amount of filter material required to achieve the desired hardness and rigidity. This in turn would allow the manufacturer to adjust the pressure drop of the filter element. This would allow a filter element according to the present invention to be designed having properties which closely resemble those of conventional CA filter elements.

Thus, the addition of a solid additive to the filter material by the methods according to the present invention can eliminate the shortcomings that are currently associated with the use of sheet filter materials, by improving the rigidity of the filter, improving the taste of the smoke, and increasing the selective removal of semi-volatile compounds. Furthermore, the combination of filter material and solid additive may provide vastly improved disintegration, dispersion and/or biodegradability of the filter element.

The methods of the invention allow the properties of non-woven sheet and paper filter materials to be fine-tuned, so that the performance of the filter element can more closely resemble that of a cellulose acetate filter element. These additives also give the use of sheet filter material much greater flexibility, widening the range of its applicability whilst retaining the beneficial biodegradable properties.

In one embodiment of the invention, the additive comprises a high molecular weight polyethylene glycol which is solid at room temperature. Suitable PEGs include PEG 600 and higher, and preferably PEG 1000 and higher.

High molecular weight polyethylene glycol has the additional advantage of providing selective removal of semi-volatile compounds. This selective removal of semi-volatile compounds provided by the addition of the PEG to the filter element is proportional to the amount of PEG included. The methods of the present invention, which involve the use a PEG which is solid at room temperature (in contrast to the PEG previously used in filters) provide flexibility which allows the addition of greater amounts of PEG than would be possible if using a liquid PEG.

This means that the ability of the filter element to selectively remove semi-volatile compounds may easily be adjusted to a desirable level. This is in contrast to the situation where low molecular weight PEG is added to cellulose acetate filters as a plasticizer. Cellulose acetate filters are generally disclosed as including less than 10% plasticizer because including higher levels of plasticizer than this has a detrimental effect on the cellulose acetate tow, causing holes to be formed. Consequently, the amount of plasticizer available to provide selective removal of semi-volatile compounds in cellulose acetate filters is limited.

According to the method of the invention, PEG may be included in the filter material of the filter element in an amount of up to about 30%, preferably up to about 20%, and more preferably about 5-10% by weight of the filter element.

As PEG is water-soluble, its inclusion in the filter elements should not adversely affect the biodegradation of the product. Indeed, it has been surprisingly found that the addition of PEG to a filter element comprising a non-woven sheet material or paper as the filter material actually enhances biodegradation.

A study was conducted to assess the effect of the use of a paper filter material and additives on biodegradability. Degradation of cigarette butts under environmental conditions was assessed. The samples used included a filter with Puracel™ (7 mg) with no additive and a filter with Puracel™ with 7% PEG 400. The results show that the inclusion of the PEG as an additive significantly increased the rate of biodegradation of the butts on a grass surface. It is speculated that this may have been due to the presence of microorganisms, insects and the like, which fed on the butts and the presence of the PEG additive made some butts more attractive. It is anticipated that a similar effect will be observed upon use of a high molecular weight PEG as an additive.

Other additives which may be used in the methods of the present invention include high molecular weight methoxypolyethylene glycols (MPEGs), such as MPEG 750, 1000, 2000, 3000 and 5000; and waxes which are solid at room temperature, including beeswax, carnauba, shellac, castor wax, paraffin and various synthetic waxes.

If desired, the method can further comprise the incorporation into the sheet filter material of further additives such as tobacco extracts, glycerine, menthol, carbon fibres, carbon particles, and the like.

A further advantage of the method of the invention is that filter elements to which additive has been applied using the claimed method are more stable to the subsequent addition of additives, including liquid additives. Other additives, including liquid additives, which would otherwise have been difficult to apply to sheet material without making it soggy, can be added to the filter rod to adjust the properties of the filter as required, or provide further qualities to the filter element, such as flavourants for enhanced flavour.

Methods according to the present invention encompass different ways of applying the additive to the filter material.

In one embodiment, the method involves applying the additive to the filter material in liquid form. In order to do this, the additive must be heated and is sprayed or otherwise applied to the filter material before the filter material is formed into the filter rod or core of the filter element.

This embodiment is attractive because it necessitates relatively little modification of conventional filter-making machinery. The only real change is the provision of means for heating the additive so that it is in molten form and may be applied to the filter material in that form. The application of the heat is relatively easy to control and monitor. Also, the application of heat is primarily just to the additive and so other components of the filter element do not need to be exposed to localised heat.

This method is applicable to both fibrous tow filter materials as well as to non-woven sheet materials and paper. Although such sheet materials are being fed under some tension, the application of the liquid additive does not weaken the sheet structure sufficiently to cause a problem.

In an alternative embodiment, the method involves applying the additive to the filter material in solid form, for example in the form of a powder, before the filter material is formed into the filter rod or core of the filter element. Once formed, the filter rod is heated to melt the additive. The additive melts and subsequently re-solidifies, bonding the filter material without making it soggy.

This method allows the additive to be applied to the filter material in a controlled and uniform manner, and with minimal wastage of additive material. It also avoids any potential disadvantages associated with applying a liquid to the filter material. For example, in the case of sheet filter materials, this embodiment avoids the potential weakening of the sheet structure by applying a liquid.

Where the solid additive is being applied to a sheet material, such as the non-woven sheet materials and papers discussed herein, steps will need to be taken to ensure that the solid additive remains in contact with the sheet filter material whilst the sheet is being fashioned into a filter rod. This may require the application of some adhesive or special orientation of the sheet material.

Filter elements comprising sheet materials are generally manufactured using a process which comprises the steps of crimping the sheet material and then gathering the sheet material to form a cylindrical filter rod. The additive may be added prior to or during the crimping process, or may be added to the sheet material after it has been crimped. The additive may even be added to the crimped material as it is gathered to form the filter rod, with the effect that it is immediately contained within the rod and does not need to be adhered.

The additive may be adhered to the filter material using any suitable adhesive, for example, using liquid starch adhesives, or EVA and PVA adhesives.

The solid additive may be applied to sheet filter material as a powder or in larger pieces, such as in the form of flakes or pellets.

The additive may be applied to the filter material by any suitable method that is known to the skilled person. For example, powdered additive may be sprayed on to the filter material, or it may be applied by an applicator which may or may not be in direct physical contact with the filter material. The additive may be loosely applied to the filter material, for example by being sprayed or sprinkled, or may be applied using a degree of force, such as by being pressed or smeared on to the filter material.

In a particular embodiment, the filter material is formed with the solid additive embedded in or on it. Applying the additive which is solid at room temperature to the filter material in this way can simplify the methods of the present invention. Once the filter material has been formed into the filter rod, the rod may be heated to melt the additive, and then allowed to re-solidify.

It is known to add various materials in or on sheet materials such as non-woven sheet materials and paper. For example, the additive may be applied to the sheet material during its manufacture or as part of a post-manufacture processing step. In this way, the additive may be incorporated within the sheet, or as a coating on one or both sides of the sheet material. The additive may be uniformly present within or on the surface of the sheet, or may be present in discreet areas, such as in patches or strips on the sheet material.

Fibrous filter material may also be prepared with particles of solid additive material dispersed throughout the fibres. Such particles may need to be adhered to the fibres. Alternatively, they may become trapped between adjacent fibres if the fibrous material is dense enough.

Where the additive is applied to the filter material in liquid form, the heating step of the method of the invention involves applying sufficient heat to the additive to ensure that the additive is molten to the extent that it has a viscosity suitable for the mode of application chosen. The molten or liquid additive may be sprayed or printed, or the filter material may be submerged in the liquid additive.

According to one embodiment, a system for applying molten or liquid additive to filter material comprises a heated chamber in which the additive is maintained in liquid form, a pump, and a hose with one or more nozzles configured to spray droplets onto the filter material prior to formation of the filter.

A number of application systems are known which are suitable for applying molten or liquid additive to filter material. Such systems are available, for example, from SPI Developments, C. B. Kaymich & Co. Ltd, or Kohl Maschinenbau GmbH.

Where the additive is to be melted after the filter material has been formed into a rod or core, sufficient heat needs to be applied to ensure that all of the additive, which is dispersed throughout the rod, is melted.

The application of heat to the formed filter rod must be carried out with care, as it may have a detrimental effect on other components of the filter rod, including the filter material and any wrapper (which is likely to be paper and could be singed or scorched by exposure to high temperatures).

Obviously, the temperature that the filter rod must be heated to, and the duration of heating, is dependent upon the melting point of the additive. A preferred additive, PEG 1000, has a melting point of around 37° C., and therefore in this case, the filter rod is heated to a temperature exceeding 37° C. The filter rod may be heated to a temperature exceeding 40° C., preferably exceeding 45° C., and most preferably exceeding 50° C. In addition, the heat needs to be applied for a period sufficient to ensure that the whole rod is heated and not just the outer areas.

Heat may be applied using any suitable means. For example, the filter rod or filter element may be brought into close proximity with a heating element. Alternatively or additionally, the filter rod or filter element may be heated by means of a current of hot gas, such as hot air or steam, or via the application of radiation, such as microwave radiation.

Heat may be applied to the filter rod as soon as it is formed. In other words, heating of the filter rod may occur at some stage between formation of the filter rod at the garniture and the cut-off, where the filter rod is separated into sections. Heating of the rod will generally be for a very brief period, such as less than 1 second, due to the linear motion of the rod through the machine. Clearly, since filter rods are currently formed without a heating process, then concomitant forming and heating of the filter rod may require expensive modification of the current apparatus.

For this reason, the filter rod is preferably heated at a later stage, and this may be achieved using a heater which is essentially separate from the apparatus involved in forming the filter rod. The heating is preferably carried out in a separate conditioning step, where lengths of filter rod are kept at an elevated temperature for an extended period of time to ensure that all of the additive is melted and bonds to the filter material.

The method of the invention may further comprise wrapping the filter rod in a suitable wrapper such as a plugwrap. In this case the heat may be applied before the filter rod is wrapped. Alternatively, the filter rod may be wrapped and then heated.

According to some embodiments, the assembled filter is heated to melt the additive, although this approach can be complicated by the insulating properties of the filter material. In addition the speed of filter manufacture means that the time available for heating the filter is limited. Having said that, heating of the assembled filter may be achieved in various ways. For example, the filter rod may be exposed to heat by conductance, such as on a heated drum in the presence of hot air. Alternatively, trays of filter rods (such as 4,000 filters per tray) may be passed through a heated tunnel or similar arrangement, in the presence of hot air. The filter trays may alternatively be heated by the application of radiation such as microwave radiation. The methods of the present invention may further comprise a step of incorporating particulate material into the filter element. Suitable particulate material includes sorbents (e.g. selected from activated carbon, charcoal, silica gel, sepiolite, alumina, ion exchange material etc.), pH modifiers (e.g. alkaline materials such as Na₂CO₃, acidic materials), flavourants, other solid additives and mixtures thereof.

Advantageously, the particulate material may be selected from a group of relatively high surface area materials capable of adsorbing smoke constituents without a high degree of specificity. Suitable general adsorbents can be selected from the group consisting of carbon, activated carbon, activated charcoal, activated coconut carbon, activated coal-based carbon or charcoal, zeolite, silica gel, meerschaum, aluminium oxide (activated or not), carbonaceous resin or combinations thereof.

One type of particulate material which may be used in the method of the invention is carbon, for instance activated carbon, or charcoal or other carbonaceous absorbent material. The preferred type of activated carbon is activated coconut carbon.

The particulate material may be incorporated into the filter element in such a way that it is interspersed throughout the filter element, or it may be interspersed in some parts (but not all) of the filter element. The particulate material may be interspersed over the full longitudinal length of the core. Alternatively, the particulate material may be interspersed from one end of the core to a section that is short of the other end. Alternatively, the particulate material may be present in discrete areas that need not extend from—or be present at—any end of the core.

Different areas may have different loadings of particulate material and/or different types of particulate material.

The methods of the present invention may further comprise wrapping the filter element in a suitable wrapper.

The wrapper of the filter element is preferably a paper wrapper, and most preferably comprises conventional plugwrap, such as plugwrap having a basis weight of between about 20 g/m² and about 35 g/m², preferably about 27 g/m². The plugwrap may be porous or non-porous.

The method may comprise the use of a wrapper which includes a particulate material adhered to one or more portions of its surface. Preferably, the particulate material is adhered to two or more portions of the wrapper, the portions being circumferentially spaced from one another, with at least one of the portions extending over the full longitudinal length of the wrapper.

The smoking article filter element produced according to the method of the present invention may be incorporated into a smoking article filter.

The smoking article filter may comprise a single filter element of the method of the invention. Alternatively, the smoking article filter may include two or more filter elements produced according to the method of the invention. In other words, the filter element may be part of a composite (or multi-component) filter. Suitably the filter elements of the composite filter are arranged longitudinally of one another with the end of each filter element abutting the next. The composite filter may have 2, 3, 4 or more distinct or discrete sections. In one embodiment the filter is a triple-filter with three sections. In another embodiment the filter is a dual-filter with two sections.

The filter sections of the composite filter may be identical, or alternatively, one or more of the sections may have a composition which is different to that of the other section or sections. For example, in some embodiments, one or more of the sections may optionally comprise: (i) cellulose acetate filter material; (ii) a biodegradable filter material, such as crepe, crimped or gathered paper material; (iii) one or more additives, such as adsorbent or flavouring materials, which may be encapsulated; and/or, (iv) a cavity, which may comprise granular material such as adsorbent material.

The smoking article filter element produced according to the method of the present invention may be incorporated into a smoking article. The filter element may be in the form of a smoking article filter as described above.

The filter element and/or filter comprising the filter element may be attached to a wrapped smokeable filler material rod (i.e. a wrapped tobacco rod, for instance) by conventional tipping overwrap to form the smoking article, which may be a cigarette.

Suitably, the smokeable filler material may be tobacco material or a tobacco substitute material. Preferably the smokeable material is a tobacco material. Suitably the tobacco material comprises one or more of stem, lamina, and tobacco dust. It is preferred that the tobacco material comprises one or more of the following types: Virginia or flue-cured tobacco, Burley tobacco, Oriental tobacco, reconstituted tobacco. It is much by preference that the smokeable material comprises a blend of tobacco material.

The smokeable filler material may also comprise one or more of the following: burn additive, ash improver, inorganic filler material, organic filler, aerosol generating means, binder, flavouring and/or colouring agents.

The tipping overwrap may be ventilating or non-ventilating overwrap.

Various modifications and variations of the described methods and system of the present invention will be apparent to those skilled in the art without departing from the scope of the present invention. Although the present invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in the art are intended to be within the scope of the following claims. 

1. A method for making a smoking article filter element comprising sheet material and an additive, wherein the method comprises the steps of: i) applying an additive which is solid at room temperature to the filter material; ii) heating the additive so as to melt it; and iii) forming the filter material and additive into a filter element, wherein the steps of the method may be carried out in any order.
 2. A method as claimed in claim 1, wherein the additive material is applied to the filter material before formation of the filter element and subsequent heating of the additive.
 3. A method as claimed in claim 1, wherein the additive is heated and applied to the filter material as a liquid, before the formation of the filter element.
 4. A method according to any one of the preceding claims, wherein the additive comprises a high molecular weight polyethylene glycol which is solid at room temperature.
 5. A method according to claim 4, wherein the polyethylene glycol is PEG
 1000. 6. A method according to any one of the preceding claims, wherein the additive is included in the filter element in an amount of up to about 50% by weight of the filter element.
 7. A method according to any one of the preceding claims, wherein the filter material is a non-woven sheet material or paper.
 8. A method according to any one of claims 1-6, wherein the filter material is a fibrous tow.
 9. A method according to any one of the preceding claims, wherein the filter element further comprises at least one adsorbent material.
 10. A filter element for a smoking article, comprising filter material and an additive which is solid at room temperature, wherein the filter element is obtained or obtainable by a method as claimed in any one of the preceding claims.
 11. A filter for a smoking article, comprising a filter element as claimed in claim
 10. 12. A smoking article comprising a filter element as claimed in claim 10 and/or a filter as claimed in claim 11, and a rod of smokeable filler material.
 13. A smoking article according to claim 12, wherein the article is a cigarette. 